The present invention relates to a method of accurately measuring, for example, a very small flying height of a slider of a magnetic disk apparatus from a magnetic disk, and to a magnetic disk apparatus adapted to be used for the measurement of the minute flying height of the slider from the magnetic disk.
Magnetic disk apparatuses are generally known as a typical example of external memory units of computers. In these apparatuses, a magnetic disk is coupled to a motor for rotation, and a slider is provided for movement above the disk. A magnetic head fixed to the slider moves together with the slider above the magnetic disk, whereby information is written in or read out of the disk.
In the conventional magnetic disk apparatuses of this type, the magnetic head and slider must be kept from being in contact with the magnetic disk so that they fly at a substantially fixed, minute height from the disk. This is required because the disk will be damaged if touched by the magnetic head. If the head fails to be kept flying a minute height above the disk, moreover, errors may possibly occur while the information is being written in or read out of the disk. Described in Japanese Patent Disclosure No. 64670/83, for example, is an apparatus in which a magnetic head and a slider are kept off a magnetic disk, flying at a substantially fixed, minute height from the disk. In this prior art apparatus, compressed air flows between the magnetic disk and the slider facing the same while the disk is rotating. An air bearing force caused by the compressed air flow acts as a dynamic lift on the slider, thereby flying the slider from the magnetic disk. At the same time, the slider is urged to be depressed toward the disk. When the force of depression balances with the dynamic lift, the head and slider fly and keep at the minute height from the disk.
Recently a recording system has been developed which can record information with high recording density. In this system, for example, magnetic domains of a magnetic disk with a perpendicular magnetic recording medium are perpendicularly magnetized so that the information is recorded on the disk. For high-density information recording on the recording system of this type, a magnetic head must be kept at a flying height of 0.1 micrometer or less from the magnetic disk, and variation of the flying height must be restricted to a very small value.
During manufacturing processes for the magnetic disk apparatuses, therefore, the flying height of the magnetic head or slider from the magnetic disk, which is very small, may sometimes suffer errors due to slight errors in assembly or slight difference in the shape of each manufactured slider. Thus, in manufacturing the magnetic disk apparatuses, the slider must be checked to see if its flying height is within a predetermined range.
Since the flying height of the slider is as small as 0.1 micrometer or less, however, it cannot easily be measured by conventional methods. The optical interference process is among the methods of measuring a minute height. However, a distance shorter than 0.1 micrometer cannot be measured directly by this process. In consequence, it is difficult to apply the optical interference process for the measurement of the flying height of the slider.
Thus, it is difficult to manufacture magnetic disk apparatuses in which the distance between the magnetic disk in rotation and the slider flying above the disk is a fixed value less than 0.1 micrometer.